Support dragging panels to stack and snap.

chrome/browser/ui/panels/native_panel.h

Index: chrome/browser/ui/panels/native_panel.h
diff --git a/chrome/browser/ui/panels/native_panel.h b/chrome/browser/ui/panels/native_panel.h
index 7d26dbbc8374ca53f0138353a30703c72dba07bf..fcb23026c4df91c82d3300955f0b2b6845fae503 100644
--- a/chrome/browser/ui/panels/native_panel.h
+++ b/chrome/browser/ui/panels/native_panel.h
@@ -78,6 +78,9 @@ class NativePanel {
   // Updates the visibility of the minimize and restore buttons.
   virtual void UpdatePanelMinimizeRestoreButtonVisibility() = 0;
 
+  // Updates the panel stacking property due to joining or leaving a stack.
+  virtual void UpdatePanelStackingProperty() = 0;

[Dmitry Titov, 2013/01/10 00:16:24]

This is needed to connect/disconnect the panel from the native stack
implementation. So it feels like a method on the NativePanelStack rather then on
the NativePanel.
Should rather be NativePanelStack::OnPanelAddedOrRemoved, if that method will
get a Panel* argument.

[jianli, 2013/01/10 02:05:37]

Done.

+
   // Create testing interface for native panel. (Keep this last to separate
   // it from regular API.)
   virtual NativePanelTesting* CreateNativePanelTesting() = 0;